1. Field of the Invention
The present invention relates to a storage system having a plurality of storage media.
2. Description of the Related Art
In a conventional storage system, a plurality of storage media are integrated, and high performance, based on parallel access, and high availability by data redundancy, are implemented using a configuration called a RAID (Redundant Array of Inexpensive Disks).
For this storage system, a storage medium called HDD (Hard Disk Drive) is normally used. An HDD is comprised of a disk called a platter where a magnetic substance for recording data is coated or deposited, a magnetic head for reading or changing the magnetic status of the platter, and a motor for rotating the platter so as to move the magnetic head onto a specified position on the platter.
Characteristics of an HDD are that access performance to the data is high, capacity is large, and cost per unit capacity is low.
In an HDD, magnetic force to handle information per unit capacity decreases naturally as the magnetic information is recorded in a micro area because of the increase of capacity. In order to detect this weakened magnetic force, the space between the platter and the magnet head must be small. This space has now reached the nanometer level.
Therefore the magnetic head may contact the rotating platter by vibration, and the platter may fail because of this contact.
Also the motor for rotating the platter is a mechanical drive component, and wears out after long periods of operation, which leads to HDD failure.
Therefore the life of an HDD is predominantly determined by the operating time.
In a storage system using an HDD, the operating time of the HDD in the storage system is recorded, and by replacing the HDD operating for a long time with a spare HDD, for example, failures are prevented so as not to lose data, and to implement high availability as shown in the method disclosed in Document 1 (Japanese Patent Application Laid-Open No. 2004-246749).